1. Field of the Invention
The present invention generally relates to a substrate processing apparatus, and more particularly to a sputtering apparatus in which large quantities of plate-like substrates having the same size are automatically processed, thereby forming a thin film on the respective plate-like substrates by means of the sputtering process. The sputtering apparatus according to the invention can provide a simple, highly reliable carrying system for the substrates, thereby improving the productivity.
2. Description of Prior Art
Various applications of the present substrate processing apparatus can be conceived. For instance, the substrate processing apparatus can be used in a thin film forming process for a silicon monolithic integrated circuit (IC). In this silicon monolithic IC manufacturing process, a metal thin film or an insulating material thin film having a thickness of approximately 1 .mu.m (micron) needs to be formed on a plurality of silicon wafers, each of the silicon wafers having for example a diameter of approximately 125 mm (millimeters) and a thickness of approximately 0.5 mm. It is known that the lower the partial gas pressure of the impurities remaining in the vacuum vessel becomes, the more superior the electrical, mechanical and physical characteristics can be obtained. It is therefore desirable to reduce a period as short as possible during which the vacuum chamber for performing the sputtering process is exposed to the atmospheric pressure. Moreover, it is desirable for the mass silicon-wafer processing to reduce the ratio of the period required for transferring/removing the wafers into/from the wafer processing apparatus as well as the exhausting period to the overall processing time. The automatic wafer processing is, on the other hand, very important to form effectively a uniform thin film on large quantities of silicon wafers at a time, by which these silicon wafers can be automatically transported without requiring manual operation. As previously described, a thin film made of a preselected material is required to be formed with a uniform thickness, because particles such as very small dust particles, cause pinholes to be formed on the substrate, where no thin film is fabricated. As a result, even if the particles are present in the vacuum chamber, the silicon wafers are preferably positioned in the vertical direction so as not to have particles accumulated thereon during the thin-film forming.
The temperature of the silicon wafer during the thin-film forming greatly influences the film characteristic. Accordingly, if one film characteristic is desirable, the temperature of the silicon wafer is heated higher than the room temperature; whereas when other film characteristics are desired, the temperatures of the silicon wafers are kept sufficiently lower than the room temperature during the film forming. As a result, when a double film layer made of two different materials is formed, the optimal wafer temperature for the first film layer is sometimes different from that of the second film layer.
Under these conventional technical aspects, various types of prior art sputtering apparatus have been proposed to automatically process silicon wafers. Among the conventional automatic sputtering apparatus, no temperature control is effected to separately control the wafer temperature of the second film layer during the continuous film forming operation. Consequently, if there exists a great difference between the respective optimum temperatures for forming the first film layer and that of the second film layer, it is very difficult to control these optimum temperatures. To the contrary, if a sufficiently long processing period is allowed to obtain optimum temperatures, this difficulty can be solved. However, such a long processing time may cause poor productivity.
When the optimum wafer temperature of the first film layer is much higher than the room temperature and the optimum wafer temperature of the second film layer is set close to the room temperature, a longer wait time in the conventional wafer forming apparatus is required until the thus heated wafer is sufficiently cooled. Thus, continuous forming of both the first and second film layers cannot be performed within a relatively short time.
A primary object of the present invention is therefore to solve the above-described conventional drawbacks and to provide a novel wafer carrying system, a holder and a temperature control mechanism for a substrate processing apparatus, by which the thin film forming can be performed on the same silicon wafers at the different temperature within a relatively short time.
A secondary object of the invention is to provide a wafer cooling mechanism with improved productivity wherein after forming the thin film on the heated silicon wafer having a higher temperature at the first stage, the thin film is formed on the silicon wafer cooled sufficiently at the second stage, taking account of the following fact. That is, in general, heating a silicon wafer is easier than cooling the heated silicon wafer in view of technical aspect.